BREAKING: Small but finite chance ISS to be hit by debris

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

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Here's the story. Today at 16:39 (UT), a small piece of space debris passed by the International Space Station. Orbit predictions put it close enough to the ISS to be a real danger, though the actual collisions odds were low. Astronauts closed all the hatches in the station and moved to the Soyuz escape module to wait it out. After the debris passed safely, they emerged, opened up all the hatches, and got back to work.

It's still not known as I write this just how close the debris passed. It was a piece of a used booster called a Payload Assist Module, a device used to boost satellites from low Earth orbit up to geosynchronous orbit. Robert Pearlman from CollectSpace told me:

This object is the "yo weight" from a Delta PAM-D stage (used to launch GPS 37 in 1993). The yo weight is a small mass attached to a 1-meter-long cable, used to tumble the stage after separation from the payload so it doesn't recontact.

The mass is probably less than 1 kg, but because it's basically a piece of string, the cross-section is large for its mass.

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A 1 kg mass moving at a relative speed of several kilometers per second could have done vast damage to the ISS, especially since it was not compact like a chunk of metal, but extended. It could have torn a huge hole in the station, and I imagine the astronauts are breathing a huge sigh of relief.

The good news here is that this object, though small, was tracked well enough to give the astronauts on the ISS plenty of time to evacuate... and don't overlook the fact that the astronauts did a great job handling the situation (whereas I would be very busy screaming and wetting myself). This was an extraordinary event handled by extraordinary people. My sincere thanks to those who took care of it, and congratulations as well.